Means for reducing eddy current heating of a tank in electric apparatus

ABSTRACT

Eddy-current heating of a tank wall is reduced by providing the tank wall with shorting members forming a secondary loop around a portion of the tank wall. One of the shorting members is located outside the tank and is a tube forming a portion of a heat pipe. This heat pipe also comprises a reservoir communicating with the tube and containing liquid refrigerant that is in good heatexchange relationship with a portion of the tank wall.

United States Patent 1191 Beatty 1 Sept. 25, 1973 1 [75] Inventor:

[ MEANS FOR REDUCING EDDY CURRENT 1 HEATING or A TANK IN ELECTRICAPPARATUS John W. Beatty, Newtown Square, Pa.

[73] Assignee: General Electric Company,

. 1 1 Philadelphia, Pa.

[22] Filed: Sept. 5,1972 21 Appl. No.: 286,470

[52] US. Cl. 174/15 R, 165/105, 174/35 CE,

[51] Int. Cl. F28d 15/00, l-lOlf 27/28 [58] Field of Search 174/15 R, 16R, 35 CE;

[56] I References Cited UNITED STATES PATENTS 3,711,622 1/1973- Deno174/35 CE 3,214.544 10/1965 Leeds 174/15 BH X 3.563.309 2/1971Basiulis... 3,595,304 7/1971 McHugh 165/105 Primary ExaminerBernard A.Gilheany Assistant Examiner-A. T. Grimlcy Attorney-J. Wesley Haubner eta1.

- ABSTRACT Eddy-current heating of a tank wall is reduced by providingthe tank wall with shorting members forming a secondary loop around aportion of the tank wall. One of the shorting members is located outsidethe tank and is a tube forming a portion of a heat pipe.'This heat pipealso comprises a reservoir communicating withthe tube and containingliquid refrigerant that is in good heat-exchange relationship with aportion of the tank wall.

8 Claims, 6 Drawing Figures PATENTED SP2 5 I975 SHEET 1 OF 2 PAIENTEBSHEET 2 OF 2 rent through the primary conductor.

MEANS FOR REDUCING EDDY CURRENT HEATING OF ATANKIN ELECTRIC APPARATUSBACKGROUND This invention relatesto electrical apparatus comprising asteel tank and a high current primary conductor extending through thetank and, more particularly, relates to means for reducing the extent towhich said tank is heated by eddy currents induced therein by curheatingof such a tank is to provide the tank with inner and outer shorting barsof high conductivity metal which are connected togetherv at their endsto-form a loop around a portion of the tank walLCurrent induced in thisloop by current in the primary conductor develops a magnetic field inthe tank wall that tends to cancel the magnetic field produced by theprimary conductor current. i I

Unfortunately, prior arrangements embodying this approach have notreduced tank heating to the extent required for certain high currentapplications. Two re- 7 gionsiof the tank where eddy current heating isespecially intense are the regions containing the usual tank end ringsthat surround the primary conductor where it passes through the tankwall. These end rings, typi cally of magnetic steel, usually surroundthe primary conductor more closely than the rest of the tank and aretherefore subject to the greatest eddy-current heating.

, SUMMARY The general object of my invention is to provide means forreducing eddy-current heating of the tank which is especially effectivein limiting the temperature rise of the aforementioned end rings.

Another object is to provide a shorting-member type ofeddy-current-heatingreducing means in which there are incorporated heatpipes for subjecting the tank end rings to vigorous cooling action. 7

Another object is to provide-a heat-pipe type of cooling arrangement forthe end rings in which a portion of the heat pipe serves not only forcooling purposes but also as part of a shorting member for reducingeddycurrent heating.

"In carrying out my'invention in one form, I provide, in combinationwith the above-described tank, a pair of shorting members, one locatedoutside and the other located inside a wall portion of the tank. Theseshorting members extend generally longitudinally of the primaryconductor and are electrically connected together at their opposite endsto form a secondary loop disposed about the tank wall portion. Meansdefining a generally annular reservoir-surrounds the primary conductorand contains liquid refrigerant that is in good heatexchangerelationship with a'tank end-ring. This refrigerant vaporizes inresponse to heating of the end ring by eddy currents induced therein 'bycurrent in the primary conductor. The outer one of the shortingmembers'is a tube communicating with said reservoir and receiving vaporsfrom the refrigerant as it vaporizes. The tube is normally in a lowertemperature region than the reservoir when the apparatus is operating,whereby the vapors contained in the tube condense therein, followingwhich they are returned from the tube to the reservoir.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of theinvention, referencemay be had to the following description taken inconjunction with the accompanying drawing, wherein:

FIG. 1 is a sectional view through a high voltage electric circuitbreaker embodying one form of the invention.

FIG. 2 is a sectional view. along the line 2-2 ofFIG.

FIG. 3 is an enlarged sectional view of a portion of FIG. 11.

FIG. 4 is an enlarged sectional view of another portion of FIG. ll. l

1 FIG. S-is a sectional view of a modified form of the invention. a v

FIG. 6 is an enlarged sectional view of a portion of FIG. 5.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to FIG. 1,there is shown an electric circuit breaker It) of the high-voltagegas-blast type, such as shown, for example, in U.S. Pat. No.3,009,983-Oppel, assigned to the assignee of the present invention. Thiscircuit breaker comprises an insulating support column 9 and, atop thecolumn, a cylindrical tank 12 of a suitable low-cost metal such as mildsteel. Tank 12 contains compressed gas at a pressure of several hundredp.s.i. At its opposite ends, tank 12 has end walls containing centrallydisposed openings through which high-voltage lead-in bushings 15 extend.

Each of these lead-in bushings comprises a centrally disposed conductivestud 20 and a tubular insulating housing 22 surrounding stud 20.Insulating housing 22 comprises a pair of tubular shells 24 and 25 ofinsulating material and a tubular intermediate portion 26 of metal,preferably aluminum, disposed between the insulating shells. The parts24, 25 and 26 of housing 22 are clamped together in a conventionalmanner, such as shown, for example, in the aforesaid Oppel patent.

Surrounding each lead-in bushing and forming an integral part of tank 12is a metal end ring 30, also preferably of mild steel. The intermediateportion 26 of the bushing fits within this end ring 30 and is suitablyattached thereto, as by bolting or by the fastening means shown in theaforesaid Oppel patent. This latter fastening means, which is bettershown in the enlarged view of FIG. 3, comprises a split locking ringfitting in an annular groove 72 in the outer periphery of bushing part26 and abutting against the inner face of the end ring 30. Suitablejackscrews 75 threaded in a flange of part 26 hold the locking ring 70against theinner face of end ring 30. The gas pressure within the tank112 also acts to hold the locking ring 70 against end ring 30.

As shown schematically in FIG. 1, disposed within tank 12 are two pairsof separable contacts connected in series-circuit relationship betweenthe inner ends of studs 20. Each pair of contacts comprises a stationary7 within the housing 32 simultaneously actuates the movablecontacts 34in one direction to open the circuit breaker and simultaneously returnsthe movable contacts to their illustrated position to close the circuitbreaker. The operating mechanism and the movable contacts areinterconnected by a mechanical linkage schematically shown at 37.

When the circuit breaker is closed as shown, current flows therethroughbetween its two terminals 40 and 42 via one stud 20, one set of contacts32, 34, mechanism housing 36, the other set of contacts 32, 34, and theother stud 20. This current path is referred to herein as the primaryconductor and the current therethrough as the primary conductor current.

In certain circuit breakers this primary conductor current may be manythousands of amperes in magnitude, even on a continuous basis. Themagnetic field produced by this high primary conductor current induceseddy currents in the steel tank 12 which tend to overheat the tank.

1 members 50'and 52, the twomembers 50, 52of each pair being connectedtogether at their opposite ends to form a loop around a portion of thetank wall. These shorting members,'which extend generally longitudinallyof the primary conductor, are ofa high conductivity metal, such ascopper, thus assuring that the loop has a relatively low resistance.

Adjacent ends of the shorting members 50 and 52 of a, given loop areelectrically connected together through the end ring 30 and asoon-to-be-described annular metallic reservoir member 60, preferably ofcopper. The annular reservoir member 60 has an inner side face 62 thatis clamped in high pressure engagement against the outer side face ofthe end ring 30 by the jackscrews 75. The mating surfaces of the endring 30 a and the reservoir member 60 are of a planar configuration andare preferably silver plated so as to impart a low thermal andelectrical resistance to the interface therebetween.

When a high conductivity loop such as S0, 52, 30, 60 is present aroundthe tank wall, a secondary current is induced in the loop which developsa magnetic field in the tank wall tending to cancel out the magneticfield developed by current through the primary conductor. The extent ofthis cancellation is increased by providing a plurality of such loopsuniformly distributed about the tank periphery, and I provide such aplurality of uniformly distributed loops, as best seen in FIG. 2; buteven with this plurality of such uniformly distributed loops present,cancellation of the magnetic field in the tank wall is still incomplete,and objectionable eddy current heating occurs when the primary currentis high.

' To limit the extent of such eddy-current heating, l construct certainof the shorting members so that they can act as heat pipes serving toextract heat from the end rings 30 of the tank. More specifically, 1construct the three outer shorting members 52 that are disposed aboutthe upper portion of tank 12 (FIG. 2) as tubes which communicate witheach of the reservoirs 60 through ports 61 located at angularly spacedpoints about the periphery of each reservoir member. in a preferred formof the invention, each tubular member 52 is constructed of two tubularsections 52a and 52b which are joined together near the mid region ofthe tubular member by a plug portion 52c that is suitably brazed at itsopposite ends to the tubular sections 52a and 52b, as is shown in detailin FIG. 4. Thus, each of these tubular members 52, while electricallycontinuous, is divided into two separate tubular sections having closedends and isolated from each other by plug portion 52c.

Each of the annular reservoir members 60 is a hollow member thatcontains an annular reservoir 64. Disposed within each reservoir 64 is anormally liquid refrigerant 65, such as Freon 1 13 (Le,trichlorotrifluorethane), which will be vaporized by heat transferred tothe reservoir member from the juxtaposed end ring 30 when high currentsflow through the primary conductor 20. When the refrigerant boils and aportion vaporizes in response to such heat, the resulting vapors passinto the tubular members 52 communicating with the space above theliquid level of the refrigerant. The tubular members 52, being outsidethe tank 12 and completely exposed to the surrounding ambient, are in arelatively cool region. The vapors within the tubular members 52therefore condense on the relatively cool walls of the tubular members,and the liquid condensate thereafter returns by gravity to the reservoir64 where it is again available for vaporization. To accelerate heattransfer from the walls of each tubular member 52 to the surroundingambient, heat-radiating fins 67, preferably of a high conductivitymaterial such as copper, are suitably joined to the tubular member onits outside surface. These fins, in combination with the highconductivity of the tube material, serve to maintain the tubular member52 relatively cool so that it can continue to act indefinitely as aneffective condenser for the vapors. It will be apparent that the parts52, 60, 64, 65 (functioning as above-described) are acting as a heatpipe, extracting heat from the end rings 30 and transferring it to thetubular portions 52. It will be further apparent that the parts 60, 52,act in a dual capacity, not only as key elements of a heat pipe, butalso as important components of the shorting-bar arrangement describedhereinabove.

While the intermediate member 26 of bushing 15 is even closer than theend ring 30 to the primary conductor 20, it will be subject to far lessheating than the end ring because it is of nonmagnetic material,preferably aluminum. To the extent that member 26 is heated, it willalso be cooled by the action of heat pipe 60, 52, 64, 65.

While the specific configuration of the tubular members 52 is notcrucial, it is highly desirable that the members be spaced from the wallof tank 12 so as to be, in effect, thermally uncoupled or insulated fromthe tank wall. Most of the heat released from the shorting member 52 cantherefore be transferred to the surrounding air without appreciablyheating the tank.

For providing mechanical support for each of the shorting members 52,spacers 66 are suitably attached to the tank wall and the shortingmembers 52 in positions between the two parts 12 and 52. Spacers 66 arepreferably, though not necessarily, of a thermal insulating material.

The shorting members 52 that are disposed about the lower portion of thetank exterior are preferably solid bars rather than being tubular as inthe case of the upper shorting members. Since these lower shortingmembers attach to the annular reservoir member 60 below the normalliquid level of the refrigerant 65, they would be filled with liquid ifthey were of the same tubular construction as the upper members 52 andcould therefore not act as vapor condensers. This being the case, andfor reasons of economics, I make these lower shorting members of asimple and inexpensive bar construction, having no passages thereincommunicating with the reservoirs.

Though described above as being applied to a horizontally extendingtank, my invention is also applicable to a vertically extending tanksuch as shown in FIG. 5. In FIG. 5, each of the shorting members 52comprises two tubular sections 52a and 52b joined together by acentrally disposed plug section 520. Two reservoir members 60 arerespectively disposed in contact with the upper and lower end rings 30.Referring to lower reservoir member 60, the lower tubular section 52a ofeach tubular member 52 communicates with its reservoir 64 adjacent thetop of this reservoir 64. Referring to upper reservoir member 60, theupper tubular section 52b of each tubular member 52 communicates withits reservoir 64 adjacent the top of its reservoir 64.

Thus, in each reservoir all the ports that connectthe reservoir to theassociated tubular members are disposed above the liquid level of therefrigerant 65v therein. Thus, each of the tubular members 520 or 52bcan receive vapors from its associated reservoir when the refrigerant inthe reservoir vaporizes and can therefore act as the condenser elementof the heat pipe.

In the lower tubular section 52a the condensate will return by gravityto its associated reservoir 64, but not in the upper tubular section52b. To return the condensate in the upper tubular sections to theirreservoir 64, I employ suitable wicks ineach tubular section 52b. Thesewicks return the condensate by capillary action to the upper reservoir64 against the force of gravity. FIG. 6 shows such wicking at 80disposed partially within tubular section 52b and partially withinreservoir 64 so that it is able to return the liquid condensate to thereservoir from the tubular section. Wicking 80 extends'along the lengthof the tubular section 52b from the position of FIG. l to its bottom.

While I have shown and describedparticular embodiments of my invention,it will be obvious to those skilled in the art that various changes andmodifications may be made without departing from my invention in itsbroader aspects; and I, therefore, intend herein to cover all suchchanges and modifications as fall within the true spirit and scope of myinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. Electric apparatus comprising:

a. a tankhaving a generally cylindrical wall portion principally ofsteel,

b. a high current primary conductor extending through the tank andsurrounded by said generally cylindrical wall portion,

c. said tank further comprising an end ring principally of steel joinedto said cylindrical wall portion and surrounding said primary conductorwhere the primary conductor enters said tank,

d. a pair of shorting members, one located outside said cylindrical wallportion and the other located inside said cylindrical wall portion,

e. said shorting members extending generally longitudinally of saidconductor and electrically connected together at their opposite ends toform a secondary loop that is disposed around said gener-' allycylindrical wall portion of the tank.

f. said shorting members being of a material having a higher electricalconductivity than the principal material of said tank wall portion,

g. means defining a generally annular reservoir surrounding said primaryconductor and containing liquid refrigerant that is in good heatexchange relationship with said end ring and that vaporizes in responseto heating of said end ring by eddy currents induced therein by currentin said primary conductor,

h. the outer one of said shorting members being a tube that communicateswith said reservoir and receives vapors from said refrigerant as itvaporizes,

. said tube normally being ina lower temperature region than saidreservoir when said apparatus is operating whereby the vapors containedin said tube condense therein,

j. and means for returning said condensed vapors from said tube to saidreservoir.

2. The electric apparatus of claim I in which:

a. said tank has two opposite ends and comprises at one end said endring of (b) claim I and comprises at its opposite end another end ringsurrounding said-primary conductor where it leaves said tank,

b. means defining another generally annular reservoir surrounds saidprimary conductor and contains liquid refrigerant that isin goodheat-exchange relationship with said other end ring and that vaporizesin response to heating of said other end ring by eddy currents inducedtherein by current in said primary conductor,

0. said tubular shorting'member comprises two tubular sections that areelectrically connected in series in said secondary loop but have theirinteriors hydraulically isolated from each other, the interior of one ofsaid tubular sections being in communication with said one reservoir toreceive vapors from said one reservoir and to return condensate thereto,and the interior of the other of said tubular sections being incommunication with the other of said reservoirs to receive vapors fromsaid other reservoir and to return condensate thereto.

3. In electrical apparatus as defined in claim ll,

a. an additional shorting member of tubular form located outside saidtank and angularly spaced about the tank periphery from said shortingmember,

b. means for electrically connecting the ends of said additionalshorting member in another secondary loop disposed around saidcylindrical tank wall portion,

c. said additional tubular shorting member communicating with saidreservoir and receiving vapors from said refrigerant as it vaporizes,

d. said additional shorting member also being in a lower temperatureregion than said reservoir when said apparatus is operating whereby thevapors contained in said additional tubular shorting member condense,and

e. means for returning the condensate from said additional tubularshorting member to said reservoir. I

4. The electrical apparatus of claim 3 in which said tubular shortingmembers communicate with said reservoir through ports that are locatedabove the normal level of liquid refrigerant in said reservoir.

5. Electrical apparatus as defined in claim 3 in which:

a. said tubular shorting members are disposed about the exterior of theupper portion of said tank,

b. an additional shorting member of bar form is disposedabout theexterior of the lower portion of said tank,

' c. said latter shorting member has no passages of the reservoir'abov'e the normal level of the liquid refrigerant in said reservoir.

7. The electrical apparatus of claim 2 in which:

a. said cylindrical tank wall portion extends generally vertically andsaid end rings are disposed at different levels,

b. each tubular section communicates with its associated reservoirthrough a port located near the top of the reservoir above the normallevel of the liquid refrigerant in said reservoir,

c. one of said tubular sections in extending away from its associatedreservoir extends downwardly, and

d. wicking is provided in said latter tubular section for returningcondensate collecting therein to said associated reservoir againstgravity forces.

8. The electrical apparatus of claim 1 in which said outer shortingmember is spaced from said cylindrical wall portion along at least aportion of the length of said outer shorting member to provide thermalinsulation between said outer shorting member and said cylindrical wallportion.

* k i t

1. Electric apparatus comprising: a. a tank having a generallycylindrical wall portion principally of steel, b. a high current primaryconductor extending through the tank and surrounded by said generallycylindrical wall portion, c. said tank further comprising an end ringprincipally of steel joined to said cylindrical wall portion andsurrounding said primary conductor where the primary conductor enterssaid tank, d. a pair of shorting members, one located outside saidcylindrical wall portion and the other located inside said cylindricalwall portion, e. said shorting members extending generallylongitudinally of said conductor and electrically connected together attheir opposite ends to form a secondary loop that is disposed aroundsaid generally cylindrical wall portion of the tank. f. said shortingmembers being of a material having a higher electrical conductivity thanthe principal material of said tank wall portion, g. means defining agenerally annular reservoir surrounding said primary conductor andcontaining liquid refrigerant that is in good heat exchange relationshipwith said end ring and that vaporizes in response to heating of said endring by eddy currents induced therein by current in said primaryconductor, h. the outer one of said shorting members being a tube thatcommunicates with said reservoir and receives vapors from saidrefrigerant as it vaporizes, i. said tube normally being in a lowertemperature region than said reservoir when said apparatus is operatingwhereby the vapors contained in said tube condense therein, j. and meansfor returning said condensed vapors from said tube to said reservoir. 2.The electric apparatus of claim 1 in which: a. said tank has twoopposite ends and comprises at one end said end ring of (b) claim 1 andcomprises at its opposite end another end ring surrounding said primaryconductor where it leaves said tank, b. means defining another generallyannular reservoir surrounds said primary conductor and contains liquidrefrigerant that is in good heat-exchange relationship with said otherend ring and that vaporizes in response to heating of said other endring by eddy currents induced therein by current in said primaryconductor, c. said tubular shorting member comprises two tubularsections that are electrically connected in series in said secondaryloop but have their interiors hydraulically isolated from each other,the interior of one of said tubular sections being in communication withsaid one reservoir to receive vapors from said one reservoir and toreturn condensate thereto, and the interior of the other of said tubularsectioNs being in communication with the other of said reservoirs toreceive vapors from said other reservoir and to return condensatethereto.
 3. In electrical apparatus as defined in claim 1, a. anadditional shorting member of tubular form located outside said tank andangularly spaced about the tank periphery from said shorting member, b.means for electrically connecting the ends of said additional shortingmember in another secondary loop disposed around said cylindrical tankwall portion, c. said additional tubular shorting member communicatingwith said reservoir and receiving vapors from said refrigerant as itvaporizes, d. said additional shorting member also being in a lowertemperature region than said reservoir when said apparatus is operatingwhereby the vapors contained in said additional tubular shorting membercondense, and e. means for returning the condensate from said additionaltubular shorting member to said reservoir.
 4. The electrical apparatusof claim 3 in which said tubular shorting members communicate with saidreservoir through ports that are located above the normal level ofliquid refrigerant in said reservoir.
 5. Electrical apparatus as definedin claim 3 in which: a. said tubular shorting members are disposed aboutthe exterior of the upper portion of said tank, b. an additionalshorting member of bar form is disposed about the exterior of the lowerportion of said tank, c. said latter shorting member has no passagestherein communicating with said reservoir, d. and means is providedconnecting said latter shorting member in another secondary loopdisposed about said generally cylindrical wall portion of the tank. 6.The electrical apparatus of claim 2 in which: a. said cylindrical tankwall portion extends generally vertically and said end rings aredisposed at different levels, b. each tubular section communicates withits associated reservoir through a port located near the top of thereservoir above the normal level of the liquid refrigerant in saidreservoir.
 7. The electrical apparatus of claim 2 in which: a. saidcylindrical tank wall portion extends generally vertically and said endrings are disposed at different levels, b. each tubular sectioncommunicates with its associated reservoir through a port located nearthe top of the reservoir above the normal level of the liquidrefrigerant in said reservoir, c. one of said tubular sections inextending away from its associated reservoir extends downwardly, and d.wicking is provided in said latter tubular section for returningcondensate collecting therein to said associated reservoir againstgravity forces.
 8. The electrical apparatus of claim 1 in which saidouter shorting member is spaced from said cylindrical wall portion alongat least a portion of the length of said outer shorting member toprovide thermal insulation between said outer shorting member and saidcylindrical wall portion.